1. Field of the Invention
The present invention relates to an image pickup apparatus which calculates a defocus amount by a phase difference detection method using an image pickup element.
2. Description of the Related Art
Previously, an image pickup apparatus which calculates a defocus amount (difference between a light receiving plane and an imaging plane formed by a lens) by a phase difference detection method (pupil-divided phase difference detection method) using an image pickup element has been known.
Japanese Patent Laid-open No. H07-318793 discloses a method of using an a-sensor array and a b-sensor array which receive incident light beams from different regions in a pupil of an image pickup optical system to obtain a correlation function while relatively shifting object images formed on the a-sensor array and the b-sensor array. Japanese Patent Laid-open No. 2008-15754 discloses a method of obtaining a shift amount to give a minimum value for continuous correlation amounts by using a method of three-point interpolation.
However, in the method disclosed in Japanese patent Laid-open NO. 2008-15754, a correct defocus amount cannot be calculated, depending on the object image (particularly, for three-dimensional object image), by using the method of three-point interpolation in some cases.